This is an application for a K08 award for Thao Dang, M.D. designed to support five-years of laboratory training to further develop her skills in molecular genetics and to explore a novel mechanism of carcinogenesis. Malignant transformation is the result of an accumulation of genetic abnormalities. Specific chromosomal translocations are a major mechanism for oncogene activation in hematopoietic malignancies, but have not been described in the much more common epithelial tumors. We have established a cell line, HCC2429, from an aggressive, metastatic lung cancer that has a normal karyotype except for a single translocation between chromosomes 15q and 19p. Using positional cloning we demonstrated that the breakpoint on chromosome 19 lies approximately 40 kb upstream from the start site of Notch3, a member of the Notch proto- oncogene family. This translocation is associated with massive overexpression of Notch3, supporting the hypothesis that the t(15;19) translocation results in the deregulation of this putative cellular proto-oncogene. Furthermore, we have also demonstrated Notch3 over-expression in a panel of lung cancer cell lines and shown that it is highly correlated with translocations involving 19p. We have therefore identified a novel recurring mechanism for oncogene activation in lung cancer as well as a putative oncogene not previously known to be involved in human cancer. Under the mentorship of Dr. David Carbone, Dr. Dang will complete the molecular characterization of the identified t(15;19) translocation, determine the spectrum of the Notch3 receptor and ligand expression in lung cancer and normal tissues, and perform studies to characterize the transforming nature of Notch3 and its effects on downstream signaling pathways in lung cancer. The research environment at the Vanderbilt Ingram Cancer Center is of exceptional caliber and will provide Dr. Dang with the opportunity to interact with experienced molecular biologists as well as geneticists. The support given by this K08 award will allow Dr. Dang to build on her existing knowledge and promote her transition to an independent investigator in a highly competitive environment.